This invention relates to glucose monitor systems and, in particular embodiments, to calibration methods for glucose monitoring systems.
Over the years, body characteristics have been determined by obtaining a sample of bodily fluid. For example, diabetics often test for blood glucose levels. Traditional blood glucose determinations have utilized a painful finger prick using a lancet to withdraw a small blood sample. This results in discomfort from the lancet as it contacts nerves in the subcutaneous tissue. The pain of lancing and the cumulative discomfort from multiple needle pricks is a strong reason why patients fail to comply with a medical testing regimen used to determine a change in a body characteristic over a period of time. Although non-invasive systems have been proposed, or are in development, none to date have been commercialized that are effective and provide accurate results. In addition, all of these systems are designed to provide data at discrete points and do not provide continuous data to show the variations in the characteristic between testing times.
A variety of implantable electrochemical sensors have been developed for detecting and/or quantifying specific agents or compositions in a patient""s blood. For instance, glucose sensors are being developed for use in obtaining an indication of blood glucose levels in a diabetic patient. Such readings are useful in monitoring and/or adjusting a treatment regimen which typically includes the regular administration of insulin to the patient. Thus, blood glucose readings improve medical therapies with semi-automated medication infusion pumps of the external type, as generally described in U.S. Pat. Nos. 4,562,751; 4,678,408; and 4,685,903; or automated implantable medication infusion pumps, as generally described in U.S. Pat. No. 4,573,994, which are herein incorporated by reference. Typical thin film sensors are described in commonly assigned U.S. Pat. Nos. 5,390,671; 5,391,250; 5,482,473; and 5,586,553 which are incorporated by reference herein. See also U.S. Pat. No. 5,299,571.
It is an object of an embodiment of the present invention to provide an improved glucose monitor system and method, which obviates for practical purposes, the above mentioned limitations.
According to an embodiment of the invention, a method of calibrating glucose monitor data includes obtaining glucose monitor data at predetermined intervals over a period of time. It also includes obtaining at least two reference glucose values from a reference source that correspond with the glucose monitor data obtained at the predetermined intervals. Additionally, calculating calibration characteristics using the at least two reference values and the corresponding glucose monitor data to regress the obtained glucose monitor data is included. And calibrating the obtained glucose monitor data using the calibration characteristics is included. In preferred embodiments, the reference source is a blood glucose meter, and the at least two reference glucose values are obtained from blood tests. In additional embodiments, the calculation of the calibration characteristics is obtained using linear regression, and in particular embodiments, using least squares linear regression. Alternatively, the calculation of the calibration characteristics is obtained using non-linear regression or a non-regression technique.
In particular embodiments, the predetermined period of time is a 24 hour period, and the predetermined intervals are 5 minute intervals. Further embodiments may include the step of shifting the data by a predetermined time factor, such as for example, ten minutes. Preferably, the calibration is performed while obtaining glucose monitor data. However, alternative embodiments may perform the calibration on glucose monitor data that has been collected for post processing by another processing device.
According to an embodiment of the invention, a method of calibrating glucose monitor data includes obtaining glucose monitor data at a predetermined memory storage rate. Also included is obtaining at least one blood glucose reference reading from a blood glucose measuring device that corresponds with at least one glucose monitor data point obtained at the predetermined memory storage rate. Calculating a calibration factor using the at least one blood glucose reference reading and the corresponding at least one glucose monitor data point is included. And calibrating the obtained glucose monitor data using the calibration factor is included. In preferred embodiments, after a first calibration factor is calculated, at least one previous calibration factor is used with at least one blood glucose reference reading from a blood glucose measuring device and its at least one corresponding glucose monitor data point to calculate a calibration factor. In additional embodiments, at least two blood glucose reference readings are used for calibration. In further embodiments, the calculation of the calibration factor is obtained using linear regression, and in particular least squares linear regression. Alternatively, calculation of the calibration factor uses non-linear regression or a non-regression technique.
In particular embodiments, the calibration factor is applied to glucose monitor data obtained before a last blood glucose reference reading from a blood glucose measuring device that corresponds with at least one glucose monitor data point obtained at a predetermined memory storage rate is used to calculate the calibration factor. Alternatively, the calibration factor is applied to glucose monitor data obtained after the last blood glucose reference reading from a blood glucose measuring device that is used to calculate the calibration factor.
In particular embodiments, the predetermined memory storage rate is once every 5 minutes. And the glucose monitor data that is obtained at a predetermined memory storage rate is the result of utilizing at least 2 sample values sampled from a glucose sensor at a rate faster than the memory storage rate.
In preferred embodiments, at least one blood glucose reference reading from a blood glucose measuring device is obtained during a predetermined calibration period, and a calibration factor is calculated using those readings after every predetermined calibration period. In particular embodiments, the predetermined calibration period is 24 hours. In further preferred embodiments, a predetermined time shift is used to temporally correlate the at least one blood glucose reference reading from a blood glucose measuring device with the at least one glucose monitor data point obtained at the predetermined memory storage rate. In particular embodiments, the predetermined time shift is ten minutes.
In particular embodiments, one or more calculations for calculating a first calibration factor is different from the one or more calculations for calculating subsequent calibration factors. In other particular embodiments, the calculation for calculating a first calibration factor uses a single-point calibration equation. In further particular embodiments, the single-point calibration equation includes an offset value. In other particular embodiments, the one or more calculations for calculating a calibration factor other than the first calibration factor uses a linear regression calibration equation, a non-linear regression calibration equation, or a non-regression technique.
According to an embodiment of the invention, a method of calibrating glucose monitor data includes obtaining glucose monitor data. It also includes obtaining from another blood glucose measuring device at least one blood glucose reference reading that is temporally associated with at least one glucose monitor data reading. Determining a calibration equation using the at least one blood glucose reference reading and the corresponding at least one glucose monitor data reading is also included. And calibrating the glucose monitor data using the calibration equation is included.
According to another embodiment of the invention, a method of calibrating body characteristic monitor data includes obtaining body characteristic monitor data. It also includes obtaining from another characteristic measuring device at least one characteristic reference reading that is temporally associated with at least one characteristic monitor data point.
Calculating calibration characteristics using the at least one characteristic reference reading and the corresponding at least one characteristic monitor data point is included. And calibrating the obtained characteristic monitor data using the calibration characteristics is included. In particular embodiments, at least two body characteristic reference readings are used for calculating the calibration characteristics. In particular embodiments, the calculation for calculating the calibration characteristics is a linear regression calculation.
According to additional embodiments of the invention, an apparatus for calibrating glucose monitor data includes a glucose monitor, glucose sensor, a blood glucose meter and a processor. The glucose monitor includes a glucose monitor memory for storing glucose monitor data. The glucose sensor is electronically coupled to the glucose monitor to supply the glucose monitor data. The blood glucose measuring device provides at least one blood glucose reference reading that is temporally associated with at least one glucose monitor data point. And the processor includes software to calculate calibration characteristics using the at least one blood glucose reference reading that is temporally associated with at least one glucose monitor data point, and the processor applies the calibration characteristics to the glucose monitor data. In particular embodiments, the at least one blood glucose reading is entered into the glucose monitor. In particular embodiments, the glucose monitor includes the processor, or alternatively, the processor is in a separate device that receives glucose monitor data from the glucose monitor.
In other embodiments of the invention, an apparatus for calibrating glucose monitor data includes means for obtaining glucose monitor data. It also includes means for obtaining from another blood glucose measuring device at least one blood glucose reference reading that is temporally associated with at least one glucose monitor data reading. Means for calculating a calibration equation using the at least one blood glucose reference reading and the corresponding at least one glucose monitor data reading is included. And means for calibrating the glucose monitor data using the calibration equation is also included.
Other features and advantages of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings which illustrate, by way of example, various features of embodiments of the invention.